1. Field of the Invention
The present invention relates to a carriage support structure for an image processing apparatus. The carriage support structure links a carriage to a tensioning member such as a wire rope, fabric or ribbon that has a high tensile strength and exhibits minimal stretching under the loads imposed in moving the carriage. The tensioning member is driven by a motor so as to move the carriage along a document containing either picture or text data for scanning the document, or for printing such data onto a blank document by a scanning process.
2. Description of Related Art
In an image reading apparatus that reads an image of a document from a sheet of paper and processes it, as with a copier or a scanner, a document is illuminated by a light source, such as a fluorescence lamp, and reflected light is received by a light receptor that is provided with an imaging lens and a photoelectric converter, such as a CCD. The imaging lens forms images onto the photoelectric converter, and mirrors are commonly used to guide the light that is reflected from the document to the light receptor. In an image reading apparatus in which the document is maintained in a fixed position, a mirror is moved along the document so that the optical path length, from the document to the light receptor, remains substantially constant while the illumination point shifts.
An example of an image reading apparatus is illustrated in FIGS. 13 and 14. FIG. 13 is a schematic perspective view of an image reading apparatus 1 on which a document is placed. The image reading apparatus includes a housing 2 having a lengthwise wall 2a on the inner surface of which two shelf-like guide plates 2b and 2e are held. A full-traverse carriage 3 and a half-traverse carriage 4 are mounted on the guide plates 2b and 2e, respectively. The carriages move in the lengthwise direction of the housing 2. The top surface of the housing 2 is covered with a platen, not shown, that is preferably made of glass and on which a document to be scanned is placed. A lamp 5, such as a fluorescent lamp, is mounted on the full-traverse carriage 3 for illuminating the document. A light receptor 20 formed of an imaging lens 6 and a photoelectric converter 7, such as a CCD, is provided in an appropriate position on a bottom plate 2c on the housing 2. A first mirror, not shown, is provided on the full-traverse carriage 3, and second and third mirrors, not shown, are provided on the half-traverse carriage 4. Light from the lamp 5 that has been reflected from the document is sequentially reflected from the first, second, and third mirrors before passing though the imaging lens 6 and entering the photoelectric converter 7. The first, second, and third mirrors define an optical path from the document to the photoelectric converter 7.
In order to obtain image information from the document, nearly the entire surface of the document has to be illuminated; therefore, the full-traverse carriage 3 is moved over nearly the entire platen. The optical path should be of a constant length while the full-traverse carriage 3 moves. To do this, the half-traverse carriage 4 moves one-half the rate of the full-traverse carriage 3 and in synchronism with it so that the optical path remains constant.
FIG. 14 is a schematic perspective view of the driving mechanism for synchronizing the movement of the carriages. A drive axis 8 is rotatably supported at one end of the housing 2 with its axis orthogonal to the scanning direction of the carriages and with a drive pulley 8a attached in the center. A motor 9 is provided on the bottom plate 2c of the housing 2. A drive pulley 9a is attached to the power axis of the motor 9. A first drive belt 11a runs over the drive pulley 9a and a first middle pulley 10a. A second drive belt 11b runs over a second middle pulley 10b integrally molded to the first middle pulley 10a and over the drive pulley 8a. In this way, the rotation power of the motor 9 is transmitted to the drive pulley 8a so that the drive axis 8 rotates at a lower speed than the motor. This results in a smooth rotation of the drive axis 8 and significantly reduces vibrations transferred to the carriages while they are being moved by the drive axis 8. Reduced vibrations are especially advantageous when downsizing the image processing apparatus. Take-up pulleys 13 are provided at both ends of the drive axis 8. The center of a tensioning member, such as a wire rope 14, is wound an appropriate number of turns around the take-up pulley 13. A pair of coaxial guide pulleys 15 and 16 are rotatably supported on the side of the half-traverse carriage 4 with their axis orthogonal to the scanning direction. At the opposite end of the housing 2 from the drive axis 8, a guide pulley 17 is rotatably supported with its axis orthogonal to the scanning direction. A bracket 2d is provided in an appropriate position on the wall 2a of the housing 2. A take-up pulley 13, a wire rope 14, guide pulleys 15, 16, and 17, and a bracket 2d are arranged on each side of the scanning region of the carriages inside the housing 2. The wire rope 14 has one end fixed to the bracket 2d and is then wound half-way around the guide pulley 16. The wire rope is then attached to the full-traverse carriage 3 by a linkage 18. The wire rope 14 then passes several times around the take-up pulley 13, passes half-way around the pulley 17 which is fixed in position relative to the housing 2, and then half-way around the guide pulley 15. The other end of the wire rope 14 then attaches to one end of a spring 19, which may be shaped as a coil. The other end of the spring 19 is attached to a sidewall of the housing 2. The linkage 18 includes a tongue 18a which projects from a base plate that forms the full-traverse carriage 3, and a screw 18b which may be threaded into the linkage 18. The wire rope 14 is clamped by the screw 18b and the tongue 18a so as to attach the wire rope 14 to the full-traverse carriage 3. Examples of the linkage structure between the full-traverse carriage 3 and wire rope 14 include the carriage fixing mechanism described in Japanese Laid-Open Patent No. 2001-092042. The linkage structure is designed to apply appropriate tension to the wire rope 14.
Japanese Laid-Open Patent No. 2001-100326 describes a photograph print apparatus that is an image reproduction scanning apparatus for forming images on a sensitized material. The photograph print apparatus projects light, including image data, onto a sensitized material in order to form an image on the sensitized material. A carriage mechanism is used to move the point from which light is projected.